CVE-2017-7520 in OpenVPN
Summary
by MITRE
OpenVPN versions before 2.4.3 and before 2.3.17 are vulnerable to denial-of-service and/or possibly sensitive memory leak triggered by man-in-the-middle attacker.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 12/29/2020
The vulnerability identified as CVE-2017-7520 affects OpenVPN implementations prior to versions 2.4.3 and 2.3.17, representing a critical security flaw that exposes systems to both denial-of-service conditions and potential memory disclosure risks. This vulnerability specifically targets the protocol handling mechanisms within OpenVPN's network communication stack, creating opportunities for malicious actors to exploit the software's response to crafted network packets. The flaw manifests when the system processes certain malformed or specially crafted packets during the authentication and key exchange phases of the VPN connection establishment process.
The technical implementation of this vulnerability stems from inadequate input validation and memory management practices within the OpenVPN codebase. When a man-in-the-middle attacker intercepts and modifies network traffic between the VPN client and server, the vulnerable software fails to properly handle certain packet structures, leading to unpredictable behavior in the memory allocation and deallocation processes. This improper handling creates conditions where the system may attempt to access freed memory locations or allocate memory without proper bounds checking, resulting in system instability or information disclosure. The vulnerability operates at the network protocol layer, specifically affecting the TLS/SSL handshake and key derivation processes that are fundamental to OpenVPN's security model.
The operational impact of CVE-2017-7520 extends beyond simple service disruption to potentially expose sensitive information stored in memory. An attacker capable of performing a man-in-the-middle position can trigger the vulnerability to cause the OpenVPN service to crash or restart, creating denial-of-service conditions that disrupt legitimate user access to network resources. More concerning is the potential for memory leakage, where the vulnerability may cause the system to inadvertently expose portions of its memory space containing sensitive data such as encryption keys, session tokens, or other confidential information. This memory disclosure risk aligns with CWE-125, which describes out-of-bounds read vulnerabilities, and CWE-476, which covers null pointer dereference conditions that can lead to information exposure.
From an adversary perspective, this vulnerability maps directly to several ATT&CK techniques including T1046 for network service scanning and T1566 for credential access through social engineering or network manipulation. The attack vector requires the presence of a man-in-the-middle position, which can be established through various means such as DNS spoofing, ARP cache poisoning, or compromised network infrastructure. The vulnerability's exploitation potential makes it particularly dangerous in environments where OpenVPN serves as a primary access control mechanism for enterprise networks, as successful exploitation could provide attackers with the means to either disrupt services or gain access to sensitive session information that could be leveraged for further attacks. Organizations should consider this vulnerability as part of their broader network security posture assessment, particularly in environments where VPN services are critical to business operations and where network traffic interception capabilities exist.
The remediation strategy for CVE-2017-7520 requires immediate deployment of patched OpenVPN versions, specifically 2.4.3 or later, and 2.3.17 or later, depending on the organization's current software version. Security teams should implement comprehensive network monitoring to detect potential exploitation attempts, including unusual traffic patterns or service disruptions that may indicate successful exploitation. Additionally, organizations should consider implementing network segmentation and additional authentication mechanisms to reduce the attack surface and limit the potential impact of such vulnerabilities. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date security software and the potential consequences of operating vulnerable network infrastructure in enterprise environments.